Higher November 2020 Paper 6 Q15
15 A bus company has a large number of buses.
25% of the buses are more than 10 years old.
If a bus is more than 10 years old, the probability that it will start first time is 0.3.
If a bus is less than 10 years old, the probability that it will start first time is 0.65.
Amir is asked to drive one of the company’s buses, chosen at random.
Calculate the probability that the bus starts first time. [4]
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| \(\frac{9}{16}\) or [0].5625 oe | 4 | B1 for 0.75 oe seen M2 for 0.25 × 0.3 + their 0.75 × 0.65 or M1 for 0.25 × 0.3 soi by 0.075 or \(\frac{3}{40}\) oe or for their 0.75 × 0.65 soi by 0.4875 or \(\frac{39}{80}\) oe | Accept [0].56 or [0].563 as final answer for full marks if B1M2 earned Award B and M marks for equivalent working with a base value e.g. 100 buses |